Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 607 PM EDT Sun Sep 27 2020 Valid 12Z Thu Oct 01 2020 - 12Z Mon Oct 05 2020 ...Overview and Guidance/Predictability Assessment... Model/ensemble guidance is agreeable and consistent in showing a closed mid level low over the Aleutians, southeast Bering Sea, and adjacent north Pacific Ocean. The low is surrounded by high amplitude ridges over eastern Asia and western Canada. The slow movement of the mean trough and closed upper low sets up a pattern where the cyclones over the next week will track over similar areas. Guidance continues to improve in the clustering of solutions with low moving north across the upper Aleutians/AK peninsula on Wed into the southeast Bering Sea/coastal southwest AK Thu morning. This means a forecasts consisting of a blend of the ECMWF/GFS/UKMET should work to mitigate minor timing/intensity differences. There is developing better agreement that on Thu morning, a triple point low develops over the north Pacific that moves north towards the AK peninsula or adjacent Kodiak Island or upper Aleutians, continuing a northwest motion into the southeast Bering Sea on Sat and occluding. There is better than average agreement among the 12z GFS, 12z ECMWF, 12z Canadian, and the 12z GEFS Mean/ECMWF Mean on the cyclone development and track. The multi-model/multi-ensemble blend was used to mitigate less than normal differences, with less weighting of the ensembles than usual. At the end of next weekend into early next week, the models are suggesting the possible development of a new cyclone in the north Pacific that would drift north and possibly make it north into the Gulf of AK on Sunday night 04 Oct into Monday 05 Oct. The 00z Canadian/GFS/ECMWF and the GEFS and ECMWF Ensemble Means are in better than average agreement on this system developing and its location on Mon 05 Oct as it approaches the southern coast. ...Weather/Threats Highlights... The pattern will favor increasing potential for heavy precipitation from the AK Peninsula to the northern Panhandle. The first surface low tracking northward towards Kodiak Island, should advect moisture into the Gulf of Alaska and eventually the southern Coast/northern Panhandle early next week, with gale force winds to locally storm force likely to accompany the cyclone. This system should produce moderate to heavy rain from the AK peninsula and Kodiak Island, the Kenai peninsula, and coastal areas east as far as the northern panhandle. The next system will likely bring another round of moderate to heavy rainfall Friday. The strength of the lows in the ECMWF, GFS, Canadian, and German ICON favor another surge of high winds and heavy rain for Kodiak Island to the southern coastal areas, including areas from the Kenai peninsula east to the northern panhandle. With the early week storm having made soils wetter or even saturated, this storm has potential to producing a flooding threat. The same would apply to the low Oct 4-5, with another wind and flooding threat possible. Expect widespread coverage of above normal lows across much of the Alaska mainland. The one area of below normal temperatures is near the upper trough in the Aleutians. Petersen Additional 3-7 Day Hazard information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html